This invention concerns apparatus and methods for laminating films. More particularly, the present invention provides apparatus and methods using vacuum to generate a laminating force.
The lamination of films often requires that pressure be supplied to force the film against a substrate to which it is to laminated. The substrate to which the film is to be laminated may be another film, a fabric, a structure (e.g., the side of vehicle, a wall, etc.) or any other object. The films are often coated with an adhesive to adhere the film to the substrate, but lamination of the adhesive-coated film under pressure often assists in providing a more secure bond between the film and the substrate. The use of pressure may also provide other advantages, e.g., reducing bubble formation, improving conformity, etc.
Although it is desirable to use pressure when laminating a film to a substrate, it can be difficult to provide enough pressure to effectively influence the lamination process. For example, when laminating two films to each other over, e.g. a roll structure, allowances must be made for deflection of the rolls because the lamination force can typically be applied only at the ends of the rolls. The result is that the size and weight of the rolls and supporting structure may be massive to compensate for roll deflection while generating sufficient and uniform pressure at the lamination point.
Another example can be found in the application of adhesive-coated plastic films, especially vinyl films, to a variety of surfaces for a variety of reasons such as advertisement, decoration, protection and the like. These surfaces can be very large in area, typically as much as 3 mxc3x9716 m. These films are adhered to very large horizontal or vertical surfaces such as walls, truck trailer sides, billboards, and the like. The films are seldom large enough to cover the entire surface with a single, integral film, so multiple films are typically used. In addition, attempts to make larger films result in films that are more difficult to handle and to register to other films. These surfaces have vast even and uneven portions, such as a truck trailer side that has flat surfaces interrupted by either corrugations or rivets, or both. These surfaces with some combination of flat portions, protrusions, and indentations require very skilled persons to adhere the film to the surfaces and then assure that such film adheres also to the protrusions or indentations, or both.
In the most common methods of applying these films, a small plastic squeegee approximately 10 cm long is typically used to manually force the film against the substrate. This is a very labor intensive process. Furthermore, this application requires skill and patience to get an application that is well adhered, free of wrinkles, and in which all films are in register.
Current techniques for treating rivets to minimize lifting involve (a) perforating the film around the rivet, (b) heating the film with a heat source, usually and hot air gun or a torch, and (c) burnishing down the film with a stiff brush, usually about 2.54 cm in diameter with 1.25 cm long bristles attached to a short wooden handle called a rivet brush. Often post-treatment with heat is used to increase bonding and further reduce stress in the film after it has been adhered to the irregular substrate. The film is typically heated while it is bridging the area around each type of surface irregularity, which can be summarized to be either a protrusion or an indentation. Because of the low mass of the film and the high temperature of the heat source, heating rates are several hundred degrees per second. Similar cooling rates are also occurring. If the film is too soft because of the heating when it is contacted with a circular motion using the rivet brush, the film is likely to be damaged. If the film is too cool, the stress is not eliminated adequately and lifting results eventually. It is therefore very difficult for one skilled in the art to assuredly adhere the adhesive-coated film to the irregular surface while the film is fully softened without damaging the film. If there is damage, the film is weakened at that location and diminishes the durability of the film. If there is an image graphic on that film, the image is marred at the damaged location. An aberration in an image, even if the image is as large as a mural on the side of truck trailer, is quite noticeable and unsatisfactory to the owner of the trailer, the marketer of a product shown in the mural on the trailer, and the graphic fabricator that has invested considerable labor and other effort to adhere the graphic film to the side of the trailer.
The present invention provides apparatus and methods for laminating films to substrates where lamination pressure is generated at least partially by a vacuum drawn in a vacuum cavity. Advantages of the apparatus and methods include the ability to provide relatively high pressures without the expected massive mechanical structures and, in addition, the uniformity of the lamination pressures across the width of the apparatus.
The apparatus and methods may be particularly useful to assist in the application of adhesive-coated plastic films, particularly vinyl films, to large area surfaces to provide improved appearance, durability, etc. Some of the most common surfaces include truck sides, walls, signs, portions of a building, vehicles, etc. These large surfaces require extensive time and labor for application of films. This often adds more cost to the project that does the film itself. Furthermore, many of these applications are on surfaces that contain compound-curved protrusions or indentations such as channels or rivets or other irregularities that increase application time and often produce wrinkles.
One problem in the art is that the application of films is being done using a small (approximately 10 cm) squeegee on very large graphics. With typical surfaces 3 meters high and 16 meters long in, e.g., truck applications and possibly much bigger for building graphics, application of the film can be very time consuming. The small rivets on the surface or series of indentations further complicate the application and are a source for wrinkles and similar defects.
The present invention solves the problem in the art by using a totally different technique, the. force generated by a partial vacuum at the interface of application, to adhere adhesive-coated films to large area surfaces. The technique is also especially effective on smaller, irregular surfaces.
In one aspect, the present invention provides an apparatus including a first end and a second end; a first roll having a longitudinal axis extending between the first and second ends; a second roll having a longitudinal axis extending between the first and second ends, wherein the second roll is spaced apart from the first roll, and further wherein the longitudinal axes of the first and second rolls are generally parallel with each other; a seal mechanism extending between the first and second ends and the first and second rolls, wherein the seal mechanism roll forms a seal with each of the first and second rolls; a vacuum cavity formed between the seal mechanism and the first and second rolls; and a vacuum port in fluid communication with the vacuum cavity.
In another aspect, the present invention provides an apparatus including a first end and a second end; a pair of first rolls including an upper and lower first roll forming a first nip, each of the first rolls having a longitudinal axis extending between the first and second ends; a pair of second rolls including an upper and lower second roll forming a second nip, each of the second rolls having a longitudinal axis extending between the first and second ends, wherein the second nip and the second rolls are spaced apart from the first nip and the first rolls, and further wherein the longitudinal axes of the first and second rolls are generally parallel with each other; an upper seal mechanism extending between the first and second ends and the upper first and second rolls, wherein the upper seal mechanism forms a seal with each of the upper first and second rolls; a lower seal mechanism extending between the first and second ends and the lower first and second rolls, wherein the lower sealing roll forms a seal with each of the lower first and second rolls; a vacuum cavity formed between the upper and lower seal mechanisms, the first and second rolls, and the lower first and second rolls; and a vacuum port in fluid communication with the vacuum cavity.
In another aspect, the present invention provides a method of laminating a film by providing an apparatus according to the present invention; locating the apparatus proximate a substrate, wherein the substrate further defines the vacuum cavity; locating a film between the substrate and at least one of the first and second rolls of the apparatus; drawing a vacuum through the vacuum port in the apparatus, wherein a negative pressure is provided in the vacuum cavity of the apparatus, wherein the first and second rolls are drawn towards the substrate; and moving the apparatus along a substrate in a lamination direction.
In another aspect, the present invention provides a method of laminating at least two continuous webs together by providing an apparatus according to the present invention; threading a first web and a second web through a first nip in the apparatus; drawing a vacuum through a vacuum port in the apparatus, wherein a negative pressure is provided in the vacuum cavity, and wherein the upper first roll and the lower first roll forming the first nip drawn towards each other, whereby a lamination pressure is provided at the first nip; and moving the first and second webs through the first nip.
Another aspect of the present invention is a method of saving labor of adhering an adhesive-coated film to a substrate, comprising (a) distributing film to a party that has been taught to use the applicator of the present invention and the method of the present invention; (b) optionally permitting such party to print an image on the film; and (c) permitting such party to use the applicator and method to adhere the film to a surface of the substrate.
A feature of the present invention is the laminator utilizes a partial vacuum, also known as negative pressure, in a vacuum cavity of the laminator to generate pressure on the laminator at the interface between the laminator and the substrate where a film is subsequently laminated. The resulting lamination pressure is essentially uniform across the lamination area because the negative pressures within the vacuum cavity are substantially equal.
When used to laminate, e.g., two or more films to each other, one advantage of the present invention is that, by relying at least partially on vacuum to generate lamination pressure, significant lamination pressures can be obtained without relying on the massive structures typically associated with pressure lamination equipment.
When used to apply graphic images and other films to, e.g., trucks, other vehicles, sign surfaces, buildings, etc., one advantage of the present invention is labor savings of such significance that the overall total cost of an image graphic film applied to a large vertical or horizontal substrate, especially one having multiple compound or irregular surfaces can be substantially reduced. Furthermore, the quality of application is significantly improved, and often, lower adhesion adhesives can be used which reduce graphic removal time. Even with the cost of film remaining constant, the labor savings reduces the total cost of application of the film by as much as 80% and reduces the total cost of the applied film on a truck trailer by as much as 40%.
When, in conjunction with vacuum, heat is used (as disclosed in, e.g., copending, commonly-assigned, U.S. patent application Ser. No. 09/236,806, filed on Jan. 25, 1999, and its continuation-in-part patent application, U.S. patent application Ser. No. 09/479,648 filed on Jan. 7, 2000), the conformability of the film around irregular or compound-curved surfaces is improved such that less aggressive adhesives can be used. These adhesives, often called removable or changeable adhesives, can save 80% of the time normally associated with removal of the graphic films. This can further cut the total cost of installed and removed applied films by as much as 60%.
With these substantial labor savings using the article and method of the present invention, one company can provide an entire product of both film goods and installation/removal services at a price considerable less than currently offered where the producer of the film goods and the installer of the film goods are unrelated companies.
Another advantage of the invention is that large sheets of film can be laminated to surfaces at high productivity of speed and assured lamination.
Another advantage of the invention is that the apparatus and methods are effective on both fabric-sided trucks and metallic-sided trucks, making one technique versatile for a graphics film installer. The fabric and the metal can both flex under the partial vacuum applied by the laminator of the present invention, improving the uniformity of the lamination pressure.
Another advantage of the invention is that the laminator can provide nearly 100% wetting area of the adhesive against the surface of the substrate whereas conventional squeegee usage can only achieve about 80% wetting. The use of a partial vacuum uses the power of a fluid to apply equal pressure at every point of contact of the film to the surface, something that is extremely difficult, if not impossible, to achieve when applying pressure with a device such as a squeegee. That advantage is even more apparent with surfaces that are filled with irregularities or compound curves or both.
As used in connection with the present invention, the term xe2x80x9cvacuumxe2x80x9d is used to describe negative pressure as compared to ambient pressure. The term does not require that an absolute or extremely negative pressure vacuum be drawn or maintained, although in some instances it may be possible and/or desirable to achieve large negative pressures in connection with the present invention.
Other features and advantages will be described below using the following drawings.